The overall goal of project HL-20846 is to characterize the various plasminogen activators present in blood using a large animal system where sufficient starting material is available for protein purification and characterization. The first year's efforts concentrated on isolation of the components of the prekallikrein fibrinolytic pathway, and assessment of this pathway's apparent potency. Since bovine kallikrein was found to be a weak activator of plasminogen alone or in combination with calcium ions, phospholipid and high molecular weight kininogen, our present emphasis has shifted to activators of much higher specific activity that can be recovered from traumatized pigs and cows. We have developed an isolation procedure on pilot scale that allows rapid purification of this activator (probably vascular plasminogen activator) in acceptable yield and are presently beginning large-scale purification from post-trauma porcine blood. The same series of precipitations followed by chromatography on lysine Sepharose works also for bovine activator, but the yield is lower. Major emphasis will be on porcine activator both for several technical reasons and because purification of pig heart activator has been reported, hopefully allowing direct comparison to the blood activator if we succeed in purifying milligram quantities of the protein.